P2PIR is one of the an application of peer to peer network. P2PIR combines key elements of File Sharing and Federal Information Retrieval. No single technique is used for all P2PIR problem. Recall and Precision are used for Evaluation of P2PIR. A field dealing with the structure, analysis, organization, storage, searching and retrieval of information is called information retrieval. And Searching in peer-to-peer networks is called Peer to Peer Information Retrieval.

1. Peer to Peer
Information Retrieval
By, Chetan K. Sundarde
@CHETANSUNDARDE
https://www.linkedin.com/in/chetansundarde
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2. Outlines :-
 Peer to Peer Network
 Information Retrieval
 Peer to Peer Information Retrieval (P2PIR)
 Peer to peer IR system architectures
 Techniques used in IR in P2P networks
 Basic algorithms used in P2PIR
 Evaluation techniques used P2PIR
 Challenges
 Conclusion
 References 29-Oct-15 2P2PIR

3. Peer To Peer Network
 Collection of distributed system
 Computers leave and join the network frequently
 Each computer acts as a server and a client simultaneously
 three tasks that every peer-to-peer network performs
 Searching: Querying and getting list of document references.
 Locating: Resolve a document reference to concrete
location - full document
 Transferring: download the document.
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4. Applications of P2P
 Information Retrieval
 File Sharing
 Gnutella, Napster, Bit-torrent, etc.
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5. Information Retrieval :-
 A field dealing with the structure, analysis, organization,
storage, searching and retrieval of information is called
information retrieval
 Search relevant documents, on the basis of user input
Document
collection
Info. need
IR
Retrieval
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6. Comparison between File Sharing and
Information Retrieval
File Sharing Information Retrieval
Application Locating Searching
Index
-Content File Identifiers Document Content
-Size Small Large
Data Exchange
-Unit File Search Result
-Size Megabyte+ Kilobyte(small)
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P2PIR- file sharing networks and federated information retrieval
P2PIR

7. Peer to peer Information Retrieval (P2PIR)
 Searching in peer-to-peer networks
 Each peer shares its information with other peer
 Peer searches information by sending queries to its peer
 Routed to one or many other peers.
 Query result is provide in the form of index
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8. Peer to peer IR system architectures
 Based on relationship between peers:
o Cooperative system
o Uncooperative system
 Based on the network structure
o Centralized network
o Structured architecture
o Unstructured architecture
 Based on task perform in P2P network
o Centralized Global Index
o Distributed Global Index
o Strict Local Indices
o Aggregated Local Indices
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9. Peer-to-Peer architectures used in IR
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G
G
G
G
G
G
G
G
G
G
L L
L
L
L
L
L
L
L
L
L
L
Central Global Index
Distributed Global Index
Aggregated Local Index Strict Local Index
P2PIR

10. Algorithm used in P2PIR
 Statistical IR algorithms
 Vector Space Model (VSM)
Document A: “books on computer networks”
Document B: “network routing in P2P networks”
Query Q: “computer network”
 Each elements of the vector corresponds to the importance of the
term in the document
 Ranking of retrieved documents based Similarity between document
vector and query vector
book
computer
network
routing
vocabulary
0.5
0.5
0.8
0
VA
0
0
0.9
0.6
VB
0
0.5
0.8
0
VQ
0.89 0.72
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11. Algorithm used in P2PIR
 Statistical IR algorithms
 Latent Semantic Indexing (LSI)
documents
terms …..
V’a V’b
semantic vectors
SVD …..
SVD: singular value decomposition
– Reduce dimensionality
– Discover word semantics
Cat <-> Pet
Bus <-> Travel
Va Vb
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P2PIR

12. Algorithm used in P2PIR…
 Distributed Hash Table (DHT)
 method of hash table lookup over a decentralized distributed network
 Key–value pairs are stored in
 Kd=hash (“books on computer networks”)
 Kq=hash (“computer network”)
 the DHT at a parent node. (Structured Architecture)
 Any node in the DHT can then efficiently retrieve the value by providing its key.
 Napster and BitTorrent
 modern DHTs are CAN, Chord, etc.
 Extend with Content-Based Search
 Full-Text Retrieval
 Content-Based Image Retrieval
 Content-Based Music Retrieval ,etc.
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13. P2P Information Retrieval Techniques
Unstructured
BFS, RBFS,
Eg.
Gnutella
Blind Search
Random
Walk
Blind Search
Routing
Indices
Indexing
Semantic
Searching
Eg. (SON)
Clustering
Structured
pSearch
Clustering
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14. Evaluation in P2P IR
 Recall (Are all the relevant documents retrieved?)
 fraction of the documents that are relevant to the query that are successfully
retrieved
 Recall = number of retrieved relevant in answer/ total number of relevant in the
collection.
 Precision (Are the retrieved documents relevant?)
 fraction of documents retrieved that are relevant to a search query
 Precision = number of retrieved relevant in answer/ number of retrieved Measure
retrieved relevant
Relevant Retrieved
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15. Evaluation Techniques in P2P IR…
 F-Score / F-measure
 Harmonic mean of precision and recall.
 Hits per Query
 average number of distinct relevant documents discovered per search query.
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16. Applications Of P2P Information Retrieval
In Real World
 YaCy (www.yacy.net)
 local index entries are injected into a distributed global index
 YaCy uses no centralized servers, but
 The resulting decentralized web search currently has about 1.4 billion documents
in its index and more than 600 peer operators contribute each month. About
130,000 search queries are performed with this network each day (Feb 2015)
 Faroo (www.faroo.com)
 This is a proprietary peer-to-peer search engine that uses a distributed global
index.
 They perform distributed crawling and ranking.
 Faroo encrypts queries and results for privacy protection.
 2 million peers.
 Some other P2PIR system: Sixearch, ODISSEA, MINERVA, Seeks, etc.
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17. Challenges:-
 Cross-Language Information Retrieval
 Maintaining index freshness
 Security features
 Quality of service
 Efficient use of resources
 Increase range of peer-to-peer network
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18. Conclusion :-
 P2PIR is one of the application of peer to peer network
 P2PIR combines key elements of File Sharing and Federal Information
Retrieval
 No single technique is used for all P2PIR problem
 Recall and Precision are used for Evaluation of P2PIR
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19. References
 ALMER S. TIGELAAR, DJOERD HIEMSTRA and DOLF
TRIESCHNIGG “Peer-to-Peer Information Retrieval ”
University of Twente, IEEE PAPER SEPT 2012.
 Rasanjalee Dissanayaka Mudiyanselage. “Ontology-based
Search Algorithms over Large- Scale Unstructured Peer-to-
Peer Networks.”Georgia State University, IEEE , OCT 2014
 Demetrios Zeinalipour-Yazti . “Information Retrieval in Peer-
to-Peer Systems .” UNIVERSITY OF CALIFORNIA RIVERSIDE,
JUNE, IEEE 2003.
 Chengye lu. “Peer to Peer English/Chinese Cross-Language
Information Retrieval.”Queensland University of Technology,
SEPT 2008.
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20. References
 Xiuqi Li and Jie Wu “Searching Techniques in Peer-to-Peer Networks.”
Florida Atlantic University Boca Raton, FL 33431, 2007
 Christos Gkantsidis, Milena Mihail, and Amin Saberi. “Random Walks in
Peer-to-Peer Networks.” Georgia Institute of Technology, Atlanta, GA,
2002.
 Taoufik Yeferny, Amel Bouzeghoub and Khedija Arour. “A QUERY
LEARNING ROUTING APPROACH BASED ON SEMANTIC
CLUSTERS.”International Journal of Advanced Information Technology
(IJAIT) Vol. 1, No.6, December 2011
 Yulian YANG . “Semantic Information Retrieval over P2P
Networks.”Universit de Lyon, CNRS INSA-Lyon, LIRIS, UMR5205, F-
69621, France, 2009.
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